* [PATCH 1/3] initramfs: move unnecessary memcmp from hot path
@ 2021-06-10 21:45 David Disseldorp
2021-06-10 21:45 ` [PATCH 2/3] initramfs: print helpful cpio error on "crc" magic David Disseldorp
2021-06-10 21:45 ` [PATCH 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
0 siblings, 2 replies; 5+ messages in thread
From: David Disseldorp @ 2021-06-10 21:45 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: David Disseldorp
do_header() is called for each cpio entry and first checks for "newc"
magic before parsing further. The magic check includes a special case
error message if POSIX.1 ASCII (cpio -H odc) magic is detected. This
special case POSIX.1 check needn't be done in the hot path, so move it
under the non-newc-magic error path.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
init/initramfs.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/init/initramfs.c b/init/initramfs.c
index af27abc59643..f01590cefa2d 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -256,12 +256,11 @@ static int __init do_collect(void)
static int __init do_header(void)
{
- if (memcmp(collected, "070707", 6)==0) {
- error("incorrect cpio method used: use -H newc option");
- return 1;
- }
if (memcmp(collected, "070701", 6)) {
- error("no cpio magic");
+ if (memcmp(collected, "070707", 6) == 0)
+ error("incorrect cpio method used: use -H newc option");
+ else
+ error("no cpio magic");
return 1;
}
parse_header(collected);
--
2.26.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 2/3] initramfs: print helpful cpio error on "crc" magic
2021-06-10 21:45 [PATCH 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
@ 2021-06-10 21:45 ` David Disseldorp
2021-06-10 21:45 ` [PATCH 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
1 sibling, 0 replies; 5+ messages in thread
From: David Disseldorp @ 2021-06-10 21:45 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: David Disseldorp
Contrary to the buffer-format.rst documentation, initramfs cpio
extraction does not support "crc" archives, which carry "070702"
header magic. Make it a little clearer that "newc" (magic="070701") is
the only supported cpio format, by extending the POSIX.1 ASCII
(magic="070707") specific error message to also cover "crc" magic.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
init/initramfs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/init/initramfs.c b/init/initramfs.c
index f01590cefa2d..19b1c70446fc 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -257,7 +257,7 @@ static int __init do_collect(void)
static int __init do_header(void)
{
if (memcmp(collected, "070701", 6)) {
- if (memcmp(collected, "070707", 6) == 0)
+ if (memcmp(collected, "0707", 4) == 0)
error("incorrect cpio method used: use -H newc option");
else
error("no cpio magic");
--
2.26.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 3/3] docs: remove mention of "crc" cpio format support
2021-06-10 21:45 [PATCH 1/3] initramfs: move unnecessary memcmp from hot path David Disseldorp
2021-06-10 21:45 ` [PATCH 2/3] initramfs: print helpful cpio error on "crc" magic David Disseldorp
@ 2021-06-10 21:45 ` David Disseldorp
2021-06-10 22:01 ` Matthew Wilcox
1 sibling, 1 reply; 5+ messages in thread
From: David Disseldorp @ 2021-06-10 21:45 UTC (permalink / raw)
To: linux-fsdevel, linux-doc; +Cc: David Disseldorp
init/initramfs.c only supports extraction of cpio archives carrying the
"newc" header magic ("070701"). Remove statements indicating support for
the "crc" cpio format.
Signed-off-by: David Disseldorp <ddiss@suse.de>
---
.../early-userspace/buffer-format.rst | 25 +++++++------------
1 file changed, 9 insertions(+), 16 deletions(-)
diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst
index 7f74e301fdf3..95e66606b605 100644
--- a/Documentation/driver-api/early-userspace/buffer-format.rst
+++ b/Documentation/driver-api/early-userspace/buffer-format.rst
@@ -14,10 +14,10 @@ is different. The initramfs buffer contains an archive which is
expanded into a ramfs filesystem; this document details the format of
the initramfs buffer format.
-The initramfs buffer format is based around the "newc" or "crc" CPIO
-formats, and can be created with the cpio(1) utility. The cpio
-archive can be compressed using gzip(1). One valid version of an
-initramfs buffer is thus a single .cpio.gz file.
+The initramfs buffer format is based around the "newc" CPIO format, and
+can be created with the cpio(1) utility. The cpio archive can be
+compressed using gzip(1). One valid version of an initramfs buffer is
+thus a single .cpio.gz file.
The full format of the initramfs buffer is defined by the following
grammar, where::
@@ -40,9 +40,9 @@ grammar, where::
In human terms, the initramfs buffer contains a collection of
-compressed and/or uncompressed cpio archives (in the "newc" or "crc"
-formats); arbitrary amounts zero bytes (for padding) can be added
-between members.
+compressed and/or uncompressed cpio archives (in the "newc" format);
+arbitrary amounts zero bytes (for padding) can be added between
+members.
The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
not ignored; see "handling of hard links" below.
@@ -55,7 +55,7 @@ by the ASCII string "000012ac"):
============= ================== ==============================================
Field name Field size Meaning
============= ================== ==============================================
-c_magic 6 bytes The string "070701" or "070702"
+c_magic 6 bytes The string "070701"
c_ino 8 bytes File inode number
c_mode 8 bytes File mode and permissions
c_uid 8 bytes File uid
@@ -68,8 +68,7 @@ c_min 8 bytes Minor part of file device number
c_rmaj 8 bytes Major part of device node reference
c_rmin 8 bytes Minor part of device node reference
c_namesize 8 bytes Length of filename, including final \0
-c_chksum 8 bytes Checksum of data field if c_magic is 070702;
- otherwise zero
+c_chksum 8 bytes Ignored; reserved for unsupported "crc" format
============= ================== ==============================================
The c_mode field matches the contents of st_mode returned by stat(2)
@@ -78,12 +77,6 @@ on Linux, and encodes the file type and file permissions.
The c_filesize should be zero for any file which is not a regular file
or symlink.
-The c_chksum field contains a simple 32-bit unsigned sum of all the
-bytes in the data field. cpio(1) refers to this as "crc", which is
-clearly incorrect (a cyclic redundancy check is a different and
-significantly stronger integrity check), however, this is the
-algorithm used.
-
If the filename is "TRAILER!!!" this is actually an end-of-archive
marker; the c_filesize for an end-of-archive marker must be zero.
--
2.26.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 3/3] docs: remove mention of "crc" cpio format support
2021-06-10 21:45 ` [PATCH 3/3] docs: remove mention of "crc" cpio format support David Disseldorp
@ 2021-06-10 22:01 ` Matthew Wilcox
2021-06-10 22:17 ` David Disseldorp
0 siblings, 1 reply; 5+ messages in thread
From: Matthew Wilcox @ 2021-06-10 22:01 UTC (permalink / raw)
To: David Disseldorp; +Cc: linux-fsdevel, linux-doc
On Thu, Jun 10, 2021 at 11:45:25PM +0200, David Disseldorp wrote:
> @@ -40,9 +40,9 @@ grammar, where::
>
>
> In human terms, the initramfs buffer contains a collection of
> -compressed and/or uncompressed cpio archives (in the "newc" or "crc"
> -formats); arbitrary amounts zero bytes (for padding) can be added
> -between members.
> +compressed and/or uncompressed cpio archives (in the "newc" format);
> +arbitrary amounts zero bytes (for padding) can be added between
> +members.
"arbitrary amounts of zero bytes", but even that doesn't sound quite
right. Maybe "arbitrary amount of zero-byte padding between members"?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 3/3] docs: remove mention of "crc" cpio format support
2021-06-10 22:01 ` Matthew Wilcox
@ 2021-06-10 22:17 ` David Disseldorp
0 siblings, 0 replies; 5+ messages in thread
From: David Disseldorp @ 2021-06-10 22:17 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: linux-fsdevel, linux-doc
On Thu, 10 Jun 2021 23:01:23 +0100, Matthew Wilcox wrote:
> > In human terms, the initramfs buffer contains a collection of
> > -compressed and/or uncompressed cpio archives (in the "newc" or "crc"
> > -formats); arbitrary amounts zero bytes (for padding) can be added
> > -between members.
> > +compressed and/or uncompressed cpio archives (in the "newc" format);
> > +arbitrary amounts zero bytes (for padding) can be added between
> > +members.
>
> "arbitrary amounts of zero bytes", but even that doesn't sound quite
> right. Maybe "arbitrary amount of zero-byte padding between members"?
Your suggestion sounds good to me. Can I squash it in with this change
for a v2, or would you prefer to handle it as a separate grammar fix?
Cheers, David
^ permalink raw reply [flat|nested] 5+ messages in thread
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